Calculation Check

[simono71]

Hi, I am a newbie, but I have done an enormous amount of reading on stepper motors recently.
Unable to resist the urge, I bought 3 small cheap stepper motors on ebay in order to convert my little proxxon mill.

The motors had no specs, so I sent an email to the manufacturers requesting specs and was told the motors were custom made and so they could not release the specs. I asked if there was anyway they could give me some information so I don't destroy the motors without giving anything proprietary away. I received the following one line email:

'Do not exceed 4 watts for the input'

The motors are Nema17, and I have determined that they are bipolar motors.

When I connect my multi-meter across any of the two coils I read 9.6 ohms

I am assuming then that using P = I squared R that the max amp rating of these motors is:

4 = I squared x 9.6

= sqrt(4/9.6)

= 0.65 A/coil

Does this seem correct, or am I misinterpreting the information?

Thanks for any guidance

[RomanLini]

4 watts per phase sounds a little hot for size 17 motors, but is probably ok if you are running a microstepping drive (not a full step drive).

Your calculation looks good.

Bear in mind the max dissipation of 4W will be with the motors mounted to a reasonable thickness of aluminium plate. You might need to de-rate the power a little bit if you have the motors mounted on something that is not a heatsink.